Wall-bounded vortex arises in both nature and various engineering applications. There have been efforts to understand the dynamics of vortices and to develop techniques to modify their behavior. Flow control is often employed to diminish the appearance of vortices or alter the characteristics of vortices in a liquid. For example, in a sump pump, the emergence of submerged vortices may degrade pump performance. If the submerged vortices are sufficiently strong, these vortices can include strong low-pressure cores, which can entrain air/vapor along their vortex cores. If such hollow-core vortices are engulfed by the pump, they can cause unbalanced loading and vibration, leading to undesirable noise and possible structural failure. Strong wall-normal vortices appear inside and outside of many fluid-based machines as well as in natural settings, including tornadoes and hurricanes.
There have been numerous attempts to introduce passive vortex control techniques to prevent the generation of the aforementioned vortices or alter their pressure distributions. Yet passive control techniques do not offer the ability to adaptively adjust the control efforts to unsteady flow conditions (beyond design conditions). Moreover, some passive control devices are difficult to manufacture. Thus, these past efforts have shortcomings in offering reliable techniques to modify the pressure distribution of these vortices. Designing a more efficient and flexible vortex control strategy remains a challenge.